Photovoltaic or solar devices, semiconductor devices, or other electronic devices are usually manufactured by utilizing a variety of fabrication processes to manipulate the surface of a substrate. Epitaxial lift off (ELO) is a less common technique for fabricating thin film devices. The ELO process provides growing an epitaxial film, layer, or material on a sacrificial layer which is disposed on a growth substrate, such as a gallium arsenide wafer. Subsequently, the sacrificial layer is selectively etched away in an acid bath, while the epitaxial material is separated from the growth substrate. The isolated epitaxial material is a thin layer or film and is usually referred to as the ELO film or the epitaxial film. Each ELO film generally contains numerous layers of varying compositions relative to the specific device, such as a photovoltaic or solar cell, a laser diode, or other electronic devices.
The growth substrates are usually crystalline wafers of gallium arsenide or other Group III/V elements. The growth substrates are very expensive, so much so as to be commercially cost prohibiting if incorporated into the finished ELO film or device. Therefore, once the ELO film has been removed during the ELO process, the growth substrates are cleaned, treated, and reused to manufacture additional ELO films.
Subsequent to the ELO process, the growth substrate usually has metallic and non-metallic contaminants adhered or otherwise deposited thereon. The growth substrate may contain metallic contaminants, such as copper contaminants at unacceptable levels, such as greater than 1×1015 metal atoms/cm2. The metallic contaminants, especially copper, if not removed from the substrate, will further contaminate ELO films which will later be formed on the growth substrate. Also, the CVD chamber and other equipment could be contaminated by the metallic contaminants and later be exposed to additional ELO films. The copper and other metallic contaminants are detrimental to the ELO films and devices which usually contain gallium arsenide materials.
Therefore, there is a need for alternative substrate cleaning methods in order to reduce or remove copper and other metallic contaminates from substrate surfaces.